1. Field of the Invention
The present invention relates to a hand tool, and more particularly to a wrench having a jaw with a wedge.
2. Description of the Prior Art
There have been two kinds of wrenches in the art. One is an adjustable wrench and the other is a solid wrench. The wrench in the art comprises a handle and a jaw. Gripping surfaces of the jaw are typically flat and face each other in parallel. Such conventional wrenches have the following disadvantages in gripping and rotating an object such as a pipe or a nut: (1) The gripping surfaces of the jaw are liable to slip along a surface of the object; (2) When the wrench works in a limited space, the wrench must be adjusted to reengage the object frequently, which decreases the efficiency; and (3) The edge of the object is likely to be damaged by a force directly applied thereto by the wrench.
In order to solve the problems of the gripping force of the conventional wrench as mentioned above, a wedge-type wrench is disclosed by Chinese Utility Model No. 9210556.7. The wrench has two jaws, each having a gripping surface. A sliding hole is provided at the each gripping surface. A cylindrical wedge connected to a spring is disposed within the sliding hole. Two teeth working surfaces of the wedges are disposed opposite each other. When used to turn a nut, the two wedges can engage the nut tightly to increase the friction and enhance the gripping force. The wrench can be adjusted to a proper position by simply turning itself to make each wedge sliding within the respective sliding hole. Thus, the wrench can successively work without a repeated operation of releasing and reengaging the nut, thereby improving the working efficiency.
However, such a wrench has some drawbacks. (1) It cannot be used for a small size object, because when the front ends of the two gripping surfaces, each configured in an arc shape, contact each other, there is a gap between the rear ends thereof. (2) Since the wedge is directly fixed in the sliding hole by a locating pin, the pin is easily damaged by a force the object exerts on the wedge during the operation. (3) As the wedge is of a cylindrical configuration, when the thickness of an object is less than half of that of the wedge, the wedge will not firmly clamp the object due to an uneven gripping force. (4) The production of the wrench requires a complex process. Two sliding holes, of which the centerline is perpendicular to each other, are to be provided in the jaws to receive the wedges and springs.